/// 制作z字行下划线
/// @param {String} $index
/// @param {Number} $count
/// @param {Number} $height
/// @param {String} $start_color
/// @param {String} $end_color
/// @author Tony Banik
/// @link https://codepen.io/tonybanik/pen/qMNGJZ

@function mixcolor(
  $index,
  $count,
  $height,
  $start_color,
  $end_color: $start_color
) {
  @if $end_color != $start_color {
    @return mix(
      $end_color,
      $start_color,
      percentage($index / (($height * 2) * $count))
    );
  } @else {
    @return $start_color;
  }
}
